The invention relates to a method of recording real time information and playback parameters related thereto on a record carrier arranged according to a recording format, in which method the real time information is subdivided into units and the playback parameters are generated and included in the units, which playback parameters comprise pointers to units located at a forward and/or backward distance relative to the unit in which the pointers are included.
The invention further relates to a device for recording real time information and playback parameters related thereto on a record carrier arranged according to a recording format, the recorder comprising processing means for subdividing the real time information into units and for generating the playback parameters to be included in the units, which playback parameters comprise pointers to units located at a forward and/or backward distance relative to the unit in which the pointers are to be included.
A method of recording real-time information on a record carrier is known from EP 814475. Real-time information is information having a real-time nature to be reproduced at a prescribed rate, usually audio or video information, or a combination of audio and video. In the known method video information is encoded digitally and subdivided into units, which are short, but independently reproducible segments of the real-time information, while corresponding audio information may be included in the units. Control information for accessing and reproducing the real-time material is generated for enabling several playback functions. A user playable program usually called a title, for example a movie, is constituted by a sequence of units and corresponding control information. Part of the control information, so called playback parameters, are included in the units to enable playback control by using information stored with the related real-time information itself, which reduces the need for memory in the player for storing control information read from separate tables, such as address lists of units. In particular, the playback parameters comprise pointers to units located at a distance in forward or backward direction, usually at fixed intervals in playback time. As the units are stored on the record carrier consecutively, said distance corresponds to a distance along the track between the unit comprising said pointers and such forward and backward units. In the event of a variable bitrate real-time signal, e.g. video after compression by MPEG2, no fixed relation exists between the distance in time and along the track. Also other data, e.g. in the event of multiplexed audio, video and text, may cause a non predictable distance along the track. So said pointers are used in jumps to other units relative to the unit just read. The user may play the movie at standard speed reading the units consecutively, but he may also scan the material in trick play modes, e.g. fast forward or reverse slow motion, using the playback parameters in the units pointing in forward and/or backward direction. The way the control information and the real-time information are provided on a record carrier is standardized to enable players of different brands to reproduce the material. An example of such a standard is the DVD-video standard, of which the relevant aspects, such as the playback parameters, are described in said EP 814475. In the known recording method the playback parameters are generated separately after the video material has been gathered and stored temporarily in a memory, e.g. on a video tape. The real-time information and control information are finally transferred to the record carrier by well known mastering and reproducing steps, e.g. pressing optical discs from a metal master disc. A problem of the known recording method is, that a temporary storage of the real-time information is required before the control information and playback parameters can be generated. On the final product, the record carrier, the playback parameters are to be positioned according to the format rules, which prescribe that the playback parameters are included in the units with the real-time information. However the playback parameters can be generated only after the real-time material is known in forward direction for a period sufficient to determine the prescribed forward pointers, and therefore a large amount of real time information needs to be stored temporarily. Hence the known method of recording is complicated and expensive, in particular in view of home recording.
It is an object of the invention to provide a recording method and device in which real-time information can be recorded according to an existing format and which is less complex.
For this purpose, the method as described in the opening paragraph is characterized in that the method comprises the steps of
buffering the real time information for a period before recording,
determining a value for at least one of said pointers based on the buffered real time information,
calculating a value for at least a further one of said pointers intended to point to a unit located at a forward distance larger than said period, based on the buffered real time information and/or a predefined value, and
recording the buffered real time information together with said determined and calculated values.
During recording some pointer values are determined as prescribed in the recording format based on buffered real-time information in a relatively small buffer. However, further values for pointers intended to point at units further away in forward direction than the period available in the buffer are calculated different from the values prescribed in the recording format. The calculated values are based on units which are present in the buffer, i.e. which are not as far away as intended, or on predefined values, e.g. indicating that a jump-address is not available. This has the effect, that a real-time recording can be made in one pass, i.e. the real-time information is recorded on a record carrier of a writable type directly at its final location without temporary storage, while the playback parameters are generated during recording.
The invention is also based on the following recognition. Formats intended for mastered and mass produced record carriers of a read-only type may prescribe a non-causal order in which playback parameters precede the recorded audio/video, because this is the order playback devices require the information for reproduction. Non-causality inherently arises during recording, because one cannot calculate pointer values for video material not yet available, in particular if the video is compressed to a variable length digital code such as MPEG2. For a professional recording studio this presents no problem, as the audio/video material is always stored in its entirety in a temporary storage device, e.g. on a master video tape, before the final authoring process is performed, in which the playback parameters are determined. In a home recorder one-pass recording is required, and therefore the DVD-video format seems unsuitable. However the inventors have seen, that playback devices respond in a predefined way to some calculated or predefined values for playback parameters which deviate from the prescribed values, for example by using a different jumping mechanism, e.g. in DVD players for fast forward a jump to a next cell is performed when the playback parameters indicate that no forward unit is available in the cell. So the prescribed playback parameters included in the units can be acceptably approached by setting the pointers pointing far forward to some calculated or predefined value. In that event the scanning mode may be somewhat faster then intended, because in said scanning mode jumps are made from cell to cell based on a cell address table present elsewhere in the DVD format, instead of the shorter jumps originally intended. The scanning mode may alternatively be somewhat slower, if the pointer values are calculated to point at existing units less far away than intended.
According to the invention the device as described in the opening paragraph is characterized as claimed in claim 5. Preferred embodiments of the method and device according to the invention are given in the dependent claims.